MI2011: Horizontal DNA Transfer Flashcards
(27 cards)
Conjugation
The one way transfer of DNA from one live bacterium to another via a pilus or chemical signalling, drawing the bacteria together and resulting in the spread of plasmid
Transformation
uptake of free DNA, in the form of plasmids or DNA released from dead bacteria closely related to the bacteria that take it up
Transduction
bacteriophage pick up genetic material from one bacterial cells and deposit it in another
What are the 5 main characteristics encoded by plasmid genes?
- Antibiotic Resistance (R)
- Colicin genes (Col)
- Degradative plasmids
- Virulence plasmids
- Conjugative Plasmids (F+)
What are the characteristics of the donor cell in conjugation of plasmids
- A plasmid carrying genetic information required for promoting DNA transfer
- Pilli
What is the F factor?
A set of tra genes in the plasmid that controls and promotes the DNA transfer from the donor cell
What components make up the tra system of the plasmid?
- origin of transfer
- origin of replication
- replication genes
- transfer of tra genes
Describe the process of conjugation in F plasmids?
See Word Document
Is the process of transformation complementarily dependent?
Yes. The uptake of free DNA is dependent upon the level of competence of recipient cells. Fully competent cells have modified cell walls and specific receptor sites on the plasma membrane that will bind free DNA.
Describe the process in which bacteriophage infect the host cell
Bacteriophage are viruses that infect bacteria and use their hosts factors for replication. They infect bacteria by attaching to specific receptors on the cell surface and injecting nucleic acid into the cell.
Lytic
No integration, replication by making progeny phage and lysing cell for release to infect (horizontal transfer)
Lysogenic
Integration into host genome, replication along with chromosomal DNA (vertical transfer)
Describe Lysogenic Cycle
- DNA molecule injected
- Brief transcription period where a repressor and an integrase are transcribed
- Repressor turns off subsequent transcription of viral DNA
- Integration into host genome
- Replication along with host
Generalised Transduction
- transfers fragments of the host DNA only
- only contains host bacterial DNA, NOT phage DNA
- transducing particles infect recipient cell
- success of transducing phage is dependent on ability to integrate into a new host
What is the result of generalised transduction?
Recombination can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells.
Specialised Transduction
- occurs with lysogenic phages
- transduction of host DNA which flanks the prophage
- results from excision error of phage DNA upon lytic trigger
- results in loss of some phage genes
Transposition
the ability of a genetic sequence to move from one location to another
Transposons
the transposable element in transposition
- do not exist independently, must shift between DNA
Transposition if mediated by an enzyme coded for by the transposable genetic element. This enzyme is called?
Transposase
A simple form of transposition that only encodes for transposase
Insertion sequences
A more complex form of transposition that encodes for several genes
composite transposons
What are the two mechanisms of transposition
Conservative and Replicative
Define conservative transposition
Transposon is cut out of DNA and inserted into new location.
Define replicative transposition
Transposon is replicated, one copy remains at original location, other is moved to new location. Donor DNA undamaged.
